1. Regulation of Blood Volume

2. Normal Value In normal healthy adults: Avg blood volume = 7% of b.w
Adults 70ml/Kg,
About 5L ( 55% plasma & 45% cells)
In normal healthy newborn: About 85ml / Kg, 1to 6 yrs 80ml / Kg,

3. Distribution of blood volume
80-84% in systemic circulation:
64% in veins
13% in arteries
7% in arterioles & capillaries
7-10% in the chambers of the heart
9-12% in pulmonary vessels

4. Physiological Variation in blood volume
Decrease
Posture- More than 30 mins of erect posture causes 15% reduction as compared to recumbent position
Increase
Age- infants
Sex
Pregnancy
Temperature
Muscular exercise

5. Pathological Variation in Blood Volume
Decrease
Haemorrhage
Burns
Anemia
Dehydration
Increase
Fluid overload
Cardiac Disease
Polycythemia

6. Measurement of Blood Volume
By indicator dilution Method
Plasma Volume (PV): 125-I labeled human serum albumin, Evan’s blue
Blood Volume= PVx100 / 100-Ht
Ht: / Red Cell volume by —
radioisotopes of 51Cr-labeled erythrocytes, ----

7. Clinical Assessment of blood Volume
Can be made in a number of ways for example:
By recording patients BP
By recording volume of peripheral pulses.
Inspection of neck veins.
A record of central venous pressure is a more accurate method.

8. Regulation of Blood Volume
Effects of deranged blood volume:
↑ BV → ↑ work load on the heart → ↑ BP, CO
Cardiac hypertrophy → cardiac failure
↓ BV → ↓ CO & BP → ↓ Tissue perfusion →
hypovolemic shock

9. Regulation of Blood Volume
is affected by:
The intrinsic mechanism for fluid exchange at the capillary membranes
&
Hormonal & Nervous influences that affect urine output & thirst mechanisms

10. Regulation ( Cont. ) Intrinsic Mechnism :
↑ BV → ↑ Capillary hydrostatic pressure &
↓ plasma colloid pressure → shift of
fluid in to tissue spaces
↓ BV → ↓ hydrostatic pressure &
↑ plasma colloid pressure →
Fluid shift into blood

11. Regulation ( Cont. )
Two main mechanisms involved in the regulation of blood volume:
1. Fluid intake--- Thirst mechanism
2. Out put– Urine output /
Neuro-humoral mechanisms underlying the above two processes

12. Thirst :
Center- Neurons in & around preoptic nucleus located in the hypothalamus.
Main stimulus:↑ Extracellular Fluid osmolarity
Other stimuli- ↓ Blood volume, ↓ BP, ↑ Angiotensin

13. Regulation ( Cont. )
In regulation of blood volume the main organ involved: Kidneys
Mechanism:
Change in volume→ Change in tonicity (sensed by osmoreceptors) & change in pressure ( sensed by pressure receptors) → Secretion of hormones ( ADH, Renin-Angiotensin, ANP, BNP)
Atrial natriuretic (peptide ANP) isolated from the heart / secreted by the heart mainly the atrial muscles & also Brain natriuretic peptide- first isolated from the brain tissue is also found in the cardiac muscle. The secretion of these two peptides is increased when NaCl intake is increased & the ECF expands. ANP & BNP in the circulation act on the kidney & increase Na excretion.

14. Osmoreceptors-ADH Feedback

16. Regulation – An Outline
Bl Osmolality Blood Volume
↑ Thirst ↓
↓ Activation of pressure receptors
↑ Water Intake ↓ ↓
ADH Renin→Angiotensin-
↑ Water reten ↓
↓ ↑ Aldosterone
↑Bl Vol & ↓Osmolality

17. Low pressure / Volume Receptors
Location- Vena cavae, Pulmonary Veins,
Atria
Stimulus- Change in wall tension
Response- affects secretion of :
ADH, Renin, Aldosterone
ANP & BNP

18. Atrial low pressure receptors (Cont.)
↑ Atrial pressure → ↓ ADH & Aldosterone Secr. ↓
↑ Vol of Urine Excretion
↓ BP
Stretching of atrial receptors → ↑ ANP Secretion
→ ↑ Water & Na Excretion

19. Low Volume Atrial Receptors (Cont.)
Response to ↓ blood volume
→ ↑ ADH Secretion
→ ↑ Sympathetic activation
→ Stimulation of Renin Secretion ( JGA ) ↓
Activation of Angiotensinogen → Angiotensin II
→ ↑ BP

20. Atrial Natriuretic peptide (ANP) & BNP
Peptides found in the heart & brain: Act on the kidneys & increase Na excretion by dilating Afferent arterioles & relaxing mesangial cells.↑ GFR &
Inhibit Na reabsorption by acting on renal tubules. Also inhibit renin secretion & counter act pressor effects of catecholamine & Angiotensin-II

21. Learning Outcomes
State normal value in an healthy adult and a new born
State fraction of blood volume present in the chambers of the heart , systemic arteries & veins, pulmonary circulation, capillaries.
Explain the determination of blood volume

22. Learning Outcomes ( Cont. )
Describe the homeostatic mechanisms responsible for regulation of blood volume
Define the term hypovolemic, describe integrated neuro-humoral responses to hypovolemia
Explain the location & functions of low pressure receptors
Analyze an outline of neural & humoral mechanisms affecting the basic role of kidneys in regulation of blood volume

23. Thank You